JP2012508640A - Spiral wire in probe of deep brain stimulator - Google Patents

Abstract

  The present invention relates to a probe for deep brain stimulation (DBS) with high total impedance but low total resistance. This is achieved because the probe has a structure with at least two interconnected helices, the two interconnected helices having different directions of rotation. A system for deep brain stimulation having the probe, power supply and electrodes is also disclosed.

Description

  The present invention relates to a probe for deep brain stimulation (DBS). In particular, the present invention relates to a probe suitable for use even under the influence of a strong external magnetic field.

  In the field of neurotechnology, deep brain stimulation (DBS) is a surgical treatment that involves the implantation of a medical device called a deep brain stimulator, which sends electrical impulses to specific parts of the brain. DBS in certain brain areas provides a great therapeutic effect for diseases that are otherwise untreatable, such as chronic pain, Parkinson's disease, tumors and dystonia. Despite the long history of DBS, its basic principles and mechanisms remain unclear. DBS directly alters brain activity in a controlled manner. Unlike the regioning technique, the effect is reversible. In addition, DBS is one of the few neurosurgical methods that allows blinded studies.

  FIG. 1 illustrates an example of a DBS system 10 according to the prior art. In principle, this DBS system has two components illustrated in FIG. 1, an implantable pulse generator (IGP) 11 and a probe 12. The IPG 11 is a battery-driven nerve stimulator that sends electrical pulses to the brain to prevent nerve activity at the target site. The IPG 11 is typically enclosed in a titanium housing, for example. A wire connects the IPG to the electrode 13 placed at the distal end of the probe. The IPG is calibrated by a neurologist, nurse or trained technician to optimize symptom suppression and control side effects.

  DBS probes are placed in the brain depending on the type of symptoms to be addressed. All components are implanted in the body by surgery. The general procedure is performed under local anesthesia where the skull is drilled and electrodes with patient feedback for optimal placement are inserted. The right side of the brain is stimulated to deal with the symptoms on the left side of the body and vice versa. FIG. 2 illustrates how the DBS system 10 is positioned in the human 21 brain. FIG. 3 illustrates how the two DBS systems 10 are positioned on the human 31 brain to stimulate both sides of the human 31 body.

  When a person with a DBS probe undergoes examination by magnetic resonance imaging (MRI), a strong electric field may occur near the end of the probe as a result of the electromagnetic field occupying the same space as the probe. This electric field induces a current that heats brain tissue. Excessive heating can destroy brain tissue. For example, for an insulated 20 cm long straight wire, it has been shown that the ambient tissue temperature can rise to 48 ° C. in the normal mode of operation of a 1.5 T MRI system. On the other hand, it is considered safe only that the temperature rise is less than 1 ° C.

  In order to solve the problem of induced current and hence the undesirable heating of human tissue, high impedance probes have been proposed. The simulation shows that the total impedance of the probe should be at least 1 kΩ for a current that should be sufficiently low according to Ohm's law.

  However, such high impedance results in a fairly limited battery life. By forming a probe with a spiral shape and a large number of electrically conducting leads, the total impedance of such a probe is the impedance of all interconnecting leads, such as parallel conducting wires. The life of the battery is increased. For example, the total impedance of 50 parallel leads each having an impedance of 1 kΩ is 20Ω.

  FIG. 4 shows an internal view of the probe 12 according to the prior art, where a number of leads 41 extend from the first end 42 of the probe to the electrode 13 placed at the distal end of the probe. . In use, the probe 40 is connected at its first end 42 to a power source and electronic device, such as an IPG, that allows current to flow through the lead 41 to the electrode 13.

  However, since these lead wires 41 have a spiral shape, high voltages and / or currents are generated in these lead wires when the probe is exposed to an external magnetic field, for example, when performing MRI. Therefore, when the spiral lead wires are exposed to an external magnetic field, there is a risk that the electronic equipment of the IPG connected to these lead wires 41 will be damaged.

  Therefore, an improved DBS probe that allows increased flexibility, cost effectiveness, sufficiently long battery life, safe operation of the electronics and prevention of excessive heating of the tissue during MRI examination is advantageous.

  Accordingly, the present invention preferably seeks to alleviate, mitigate or reduce one or more of the above technical disadvantages and disadvantages, one at a time or in combination, and at least solve the above-mentioned problems, for example, deep brain stimulation ( The solution is to provide a probe for DBS).

  In some embodiments, the probe has multiple leads that form a structure. This structure has at least two interconnected helices, which have different directions of rotation.

  This provides the advantage that the probe is used with an external magnetic field with a change in polarity without overheating the surrounding tissue. The different directions of rotation of these helices also prevent the generation of high voltages and / or currents on the leads when the probe is exposed to an external magnetic field, for example when performing MRI. Thereby, the safe operation | movement of the electronic device connected to a probe is achieved. Furthermore, it allows for increased flexibility, cost effectiveness and sufficiently long battery life.

  In another aspect, a system for deep brain stimulation having the probe is provided.

  In yet another aspect, a pacemaker system having the probe is provided.

  In another aspect, a muscle stimulation system having the probe is provided.

  In yet another aspect, a system for gastrointestinal stimulation having the probe is provided.

  In yet another embodiment, the use of a probe for deep brain stimulation is provided.

  Other embodiments and advantages are described in further detail below.

Explanatory drawing of an example of the DBS system by a prior art. Explanatory drawing of how a DBS system according to the prior art is positioned on the human brain. An illustration of how two DBS systems are positioned in the human brain to stimulate both sides of the human body. Explanatory drawing of the internal view of the probe by a prior art. Explanatory drawing of the internal view of the probe by an Example. The internal explanatory drawing of rotation in a part of probe by an example. Explanatory drawing of the probe by this invention connected to an implantable stimulus generator (IPG). Explanatory drawing which shows the rotation by a certain Example. Explanatory drawing which shows the rotation by a certain Example. Explanatory drawing of the cross section of the probe by a certain Example.

  These and other aspects, features and advantages of the present invention will be apparent from and will be elucidated with reference to the accompanying drawings from the following description of embodiments of the invention.

  Several embodiments of the present invention are described in more detail below with reference to the accompanying drawings in order to enable those skilled in the art to practice the invention. However, the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. These examples do not limit the invention, which is limited only by the scope of the appended claims. Moreover, the terminology used in the detailed description of specific embodiments illustrated in the accompanying drawings is not intended to be limiting of the invention.

  The following description focuses on examples applicable to deep brain stimulation.

  In the embodiment according to FIG. 5, a probe 50 for deep brain stimulation is provided. The probe 50 has a large number of lead wires forming the structure 51. The structure 51 has at least two interconnected helices 52, 53, wherein the at least two helices 52, 53 have different rotational directions. The advantage of this embodiment is that when a human with an implantable BDS probe is exposed to an external magnetic field with a change in polarity, eg when performing magnetic resonance imaging (MRI), this structure is desirable for human tissue. There is no heating to reduce.

  FIG. 6 illustrates in more detail how in the probe 50 of FIG. 5 at least two helices 52, 53 are interconnected according to an embodiment.

  The mechanical stability of the structure 51 and the spirals 52, 53 is achieved in several ways. In one embodiment, the structure 51 is covered with a thermoplastic layer that forms an adhesive bond by heating, such as obtained by passing a current through the spirals 52, 53, while the spirals 52, 53 are In contact with the thermoplastic material. The thermoplastic material melts with the heat of the helix and forms a layer around the helices 52, 53 as the material cools, thus adding stability to the structure 51.

  In the embodiment according to FIG. 7, the probe 50 is connected to an implantable pulse generator (IPG) for allowing current to flow through the lead to the electrode 72 of the probe 50. The advantage of this embodiment is that the risk of damaging the electrodes in the IPG is dramatically reduced when the probe is exposed to an external magnetic field, for example when performing magnetic resonance imaging. The shape of this structure minimizes the high voltage and / or current generated in the lead due to the external magnetic field.

  A single dielectric (inductor) captures a dynamic magnetic field, whereas a double dielectric with a loop wound oppositely does not capture a dynamic magnetic field. Therefore, a strong current that breaks the IPG electronic device is not generated from the external magnetic field accompanied by the polarity change.

  In one embodiment, the direction of rotation of the structure changes at an intermediate point.

  In one embodiment, the direction of rotation of the structure changes several times.

  In some embodiments, the number of leads is greater than the actual number of leads used to stimulate tissue. This selects a subset of the leads for use and connects them to the probe electrodes. In one embodiment, the number of leads is 64, and 8 leads are selected for connection to the electrodes of the DBS probe. This has the advantage of spatially handling the best brain region for the probe to stimulate.

  In the embodiment according to FIG. 8, the leads forming the structure 51 are tracks on a foil such as a thin foil having a thickness of less than 1 mm. FIG. 8A shows the foil in a flat shape, and FIG. 8B shows the foil configured as interconnected helices 51, 52, where the helices 51, 52 have different rotational directions.

  The properties of the foil are described in further detail below. The advantage of this embodiment is that different rotational directions are easily achieved. Furthermore, when using foil, the number of turns required may be small.

  According to another embodiment, the lead is a wire. These wires may be individual and insulated. The properties of the wire are further described below. The advantage of using separate and insulated wires is that they are as thin as, for example, about 25 μm and therefore provide a low DC resistance.

  In the embodiment according to FIG. 9, it is shown how individual circular wires 91 are incorporated in a single cable 92. This is a cross section of a helically or rotated cable. The shape is a high density packing, which relatively reduces the external dimensions of the combined wire.

  In one embodiment, the wires are twisted together before spiraling along the probe to prevent local portions of the wires from having the same relative position to each other in space. This change in relative position due to the twisting of the wires reduces the capture of an external magnetic field, such as an MRI RF field. Other embodiments are disclosed in the following non-limiting examples.

Examples The following examples are carried out using either an embodiment with foil or an embodiment with individual wires. However, this should never be considered limiting.

  At MRI frequencies, typically 40-128 MHz, spiral probes have sufficiently high impedance as a result of high self-inductance, while at DBS stimulation frequencies, typically frequencies below a few kHz, the impedance is DC resistance. This resistance is low enough to limit power loss.

  According to one embodiment, the impedance of all probes at the MRI frequency is above 1 kΩ, while the effective DC resistance is below 100 Ω.

  According to one embodiment, the impedance of all probes at the MRI frequency is above 1 kΩ, while the DC resistance of each lead is several kΩ, for example below 5 kΩ.

により与えられる。ここでＲ＝らせん状導体の（ＤＣ）抵抗、ｆ＝（１．５ＴのＭＲＩシステムに対し６４ＭＨｚである）周波数、及びＬ＝らせん状導体のインダクタンス、である。 The absolute value Z of the spiral conductor impedance is given by the following equation:

Given by. Where R = (DC) resistance of the helical conductor, f = frequency (which is 64 MHz for a 1.5T MRI system), and L = inductance of the helical conductor.

により与えられる。 If the required impedance at the MRI frequency is above 1 kΩ and the resistance is below 100 Ω, then all the impedance of this helical conductor is approximately equal to the impedance of the inductance, which is

Given by.

により概算され、ここでＮ＝巻き数、μ_０＝真空の透磁率＝４π・１０^−７Ｈ／ｍ、ｒ＝ソレノイドの半径、ｌ＝ソレノイドの長さ、である。 The inductance L of a thin wall finite length solenoid of radius r and length l made of circular wire is given by the following equation:

Where N = number of turns, μ ₀ = vacuum permeability = 4π · 10 ⁻⁷ H / m, r = solenoid radius, l = solenoid length.

により与えられる。 As a result, the number of turns N required to achieve impedance Z is equal to

Given by.

  According to one embodiment, where Z = 1 kΩ, r = 0.6 m, l = 10 cm and f = 64 MHz, this results in N = 420.

  However, for small dimensions, including when working with DBS probes, it is common to use very thin leads, for example about 0.1 μm. This makes it more complicated to approximate the impedance using a simple equation as described above. As a result, 3D electromagnetic simulations have been performed using varying turns of a 10 cm long solenoid. Simulations described in detail below show that about 250 turns are sufficient for a flat helical conductor.

  The 3D electromagnetic simulation is performed using a program 3D electromagnetic simulation Micro Wave Studio by CST (www.sct.com) according to a method well known to those skilled in the art. This program is based on a finite integration technique, which demonstrates the consistent transformation of Analytic Maxwell's equations into a set of matrix equations. The probe is modeled as a 10 cm long solenoid with a width of 0.1 mm, preferably a conductive wire. In the simulation, the probe is positioned in a 4 cm × 4 cm × 14 cm uniform box with electrical parameters representing parameters in the human brain at the MRI frequency. For an MRI frequency of 64 MHz, the relative dielectric constant is set to 100 and the conductivity is set to 0.5 S / m. At the boundary of the computational domain, the electromagnetic field of the incident plane wave is imposed with an electric field component parallel to the probe axis. In the case of a 3D simulation program, the current density is calculated in the material surrounding the probe (indicating brain tissue). The maximum current density is taken as an evaluation criterion. As mentioned above, the simulation shows that the maximum current density is greatly reduced when the number of turns is increased to 250 turns over 10 cm. In the case of 250 turns, the current density induced near the end of the probe is sufficiently suppressed.

により計算される。 Another important factor to consider is wire resistance. This is illustrated in the following example using an example using foil. The resistance of this wire is estimated according to: If these wires are in the form of a foil spirally wound around the probe,
l ₀ = probe length,
l = total length of coil foil,
r = radius of the probe (ie coil radius),
w = foil width,
p = coil pitch,
N = number of turns,
R = resistance of each wire, and the total length of the foil of the coil is

Is calculated by

である。 If the pitch p is equal to the foil width w (ie every turn is next to the next),

It is.

と書かれる。ここでρ＝材料の導電率、ｔ＝薄膜の導体の厚さ、ｎ＝各フォイルにおける導電ワイヤの数、である。 Each wire in the foil is a thin film conductor and its resistance is

It is written. Where ρ = material conductivity, t = thickness of thin film conductor, n = number of conductive wires in each foil.

である。 In addition, if the foil is wrapped around the probe in a non-spiral manner (the wire is straight along the probe)

It is.

である。 Therefore,

It is.

For example, for l ₀ = 15 cm and r = 0.6 mm, the results according to Table 1 are achieved.

  Table 1 shows that by winding the foil in a spiral around the probe, the resistance of the individual wires increases with the number of turns. When the number of turns is small, DC resistance increments are still acceptable for power consumption requirements. However, if 250 turns are required, the DC resistance will be too high.

  In one embodiment, instead of foil interconnections, 64 individual insulated wires are used. At this time, a fairly low DC resistance is achieved, as shown below. The greater the number of wires, the more individual electrodes can be handled. This allows the physician to successfully determine which part of the brain tissue is stimulated. Therefore, while the number of wires used varies, they must be large enough to provide enough individual electrodes while at the same time being small enough to provide low DC resistance. I have to do something.

を用いて計算され、これは、抵抗要件を満たし、実用的なバッテリーの寿命を達成する。 For a 15 cm long probe with 250 turns, the pitch is 600 μm. If each individual wire is a gold microwire with a diameter of 25 μm, 64 wires will easily mate with a cable with a diameter of 600 μm. This cable may be about 950 mm long. The DC resistance of each wire is

Which meets the resistance requirement and achieves practical battery life.

  Accordingly, in one embodiment, the helix has 64 parallel wires. These wires are individually and insulated. These wires may be rectangular or circular.

  In one embodiment, only two groups of eight parallel wires are electrically driven by two circuits in the IPG. The remaining wires are passively connected to the IPG ground and therefore form an electrical circuit. In one embodiment, the remaining wires are connected to the IPG through resistors.

  According to one embodiment, the helix has a foil with 64 parallel tracks. The advantage this has is that it is easy to manufacture the helix.

  In one embodiment, the system may include a probe with multiple leads that form a helix whose spiral rotation is reversed. Such a system may be a system for DBS, pacemaker, muscle stimulation or gastrointestinal stimulation, for example. Features according to other embodiments described above may be included in the system.

  The probe with multiple leads forming a helix whose spiral rotation is reversed may be used for deep brain stimulation. Further, the probe may be used for pacemaker stimulation, muscle stimulation or gastrointestinal stimulation.

  Either the DBS probe is configured with a separate return electrode or the IPG housing serves as an electrical contact with brain tissue for return current. Thus, when a probe according to certain embodiments is used, current flows from the IPG through the helix, through contacts at the end of the probe, through human tissue, and back to the return electrode or IPG housing.

  Although the present invention has been described above with reference to specific embodiments, it is not intended that the invention be limited to the specific form set forth herein. Rather, the invention is limited only by the accompanying claims and, other embodiments than the specific embodiments described above are equally possible within the scope of these appended claims.

  In the claims, the word “comprising / including” does not exclude the presence of other elements or steps. Further, even if individual features are included in different claims, these features may be advantageously combined in some cases, and inclusion of different features in different claims is not feasible and / or It does not mean that it is not advantageous. In addition, not mentioning a plurality does not exclude a plurality. The words “one”, “some”, “first”, “second” and the like do not exclude a plurality. Reference signs in the claims are provided merely as a clarifying example and shall not be construed as limiting the scope of the claims in any way.

Claims (14)

  Probe for deep brain stimulation having multiple leads forming a structure having at least two interconnected helices, the two interconnected helices having different rotational directions .   The probe of claim 1, wherein at least one lead at the first end is connected to a power source that allows current to flow through the lead during use.   The probe according to claim 1, wherein the rotation direction of the structure changes at an intermediate point.   The probe according to claim 1, wherein the rotation direction of the structure changes several times.   The probe according to claim 1, wherein the lead wire is a track on a foil.   The probe according to claim 1, wherein the lead wire is an individual wire.   The probe according to claim 6, wherein a plurality of wires are collected in a single cable to form the at least two helices.   The probe according to claim 6, wherein the wires are twisted together before forming the at least two helices.   The probe of claim 1, wherein the number of leads is greater than the actual number of leads used to stimulate tissue.   A system for deep brain stimulation comprising the probe according to claim 1, a power source and an electrode.   A pacemaker system comprising the probe according to claim 1, a power source, and an electrode.   A muscle stimulation system comprising the probe according to claim 1, a power source, and an electrode.   A system for gastrointestinal stimulation comprising the probe of claim 1, a power source and an electrode.   Use of the probe for deep brain stimulation according to claim 1.

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